Class "SpatialPolygons"
SpatialPolygons-class.Rdclass to hold polygon topology (without attributes)
Objects from the Class
Objects can be created by calls to the function SpatialPolygons
Slots
polygons:Object of class "list"; list elements are
all of class Polygons-class
plotOrder:Object of class "integer"; integer array
giving the order in which objects should be plotted
bbox:Object of class "matrix"; see Spatial-class
proj4string:Object of class "CRS"; see CRS-class
Extends
Class "Spatial", directly.
Methods
Methods defined with class "SpatialPolygons" in the signature:
signature(obj = "SpatialPolygons"): select subset of (sets of) polygons; NAs are not permitted in the row index
signature(x = "SpatialPolygons", y = "missing"):
plot polygons in SpatialPolygons object
signature(object = "SpatialPolygons"): summarize object
signature(object = "SpatialPolygons"): rbind-like method
plot method arguments
The plot method for spatial polygons takes the following arguments:
a SpatialPolygons object
a vector of colour values
default par("fg"); the colour to draw the border
default FALSE; if TRUE, add to existing plot
default NULL; ranges for the plotted ‘x’ and ‘y’ values
default NULL; controls clipping, see par
default NULL; the density of shading lines, in lines per inch, see polygon
default 45; the slope of shading lines, given as an angle in degrees (counter-clockwise), see polygon
default NULL, set to par("bg") by default “transparent”; the colour to paint holes
default FALSE; draw axes
default par("lty"); border line type
other arguments passed through
default FALSE; see Spatial-class for further details
default NULL to set from option value; use polypath for hole-handling in plot
default NULL to set from option value; character value specifying the path fill mode, see polypath
The options for usePolypath and rule may be retrieved with get_Polypath (default TRUE on package load) and get_PolypathRule (default “winding” on package load), and set with set_Polypath and set_PolypathRule
The class definitions used for polygons in sp do not accord with those of
the simple features specification of the Open Geospatial Consortium. The rgeos package, an interface to Geometry Engine -- Open Source (GEOS), uses this
specification, in which each hole (interior ring) must be associated with
its containing exterior ring. In order to avoid introducing incompatible
changes into the class definition of Polygons objects, a comment has been
added as a single character string to each such object. Here we can trust
the data source to assign the hole status correctly, and use the simple
function createSPComment to add such comments to each Polygons member of
the polygons slot of this SpatialPolygons object. Exterior rings are coded
zero, while interior rings are coded with the 1-based index of the
exterior ring to which they belong. SpatialPolygons objects created by reading using readOGR from rgdal have the comments set on input, as OGR also uses SFS.
Refer to Bivand et al. (2013), pages 47-48 and 132-133 for a further discussion.
Note
rbind calls the function SpatialPolygons, where it is
checked that all IDs are unique. If rbind-ing SpatialPolygons without
unique IDs, it is possible to set the argument makeUniqueIDs = TRUE, although
it is preferred to change these explicitly with spChFIDs.
References
Roger Bivand, Edzer Pebesma and Virgilio Gomez-Rubio, 2013. Applied spatial data analysis with R, Second edition. Springer, NY. https://asdar-book.org/
See also
Examples
# simple example, from vignette("sp"): Sr1 = Polygon(cbind(c(2,4,4,1,2),c(2,3,5,4,2))) Sr2 = Polygon(cbind(c(5,4,2,5),c(2,3,2,2))) Sr3 = Polygon(cbind(c(4,4,5,10,4),c(5,3,2,5,5))) Sr4 = Polygon(cbind(c(5,6,6,5,5),c(4,4,3,3,4)), hole = TRUE) Srs1 = Polygons(list(Sr1), "s1") Srs2 = Polygons(list(Sr2), "s2") Srs3 = Polygons(list(Sr3, Sr4), "s3/4") SpP = SpatialPolygons(list(Srs1,Srs2,Srs3), 1:3) plot(SpP, col = 1:3, pbg="white")
